Nowadays, in a mobile phone terminal and a mobile network, employing the third generation W-CDMA (Wideband Code Division Multiple Access) technology, video phone (TV telephone) services are implemented using a mobile circuit switched network and a protocol for circuit switching in accordance with the 3G-324M specifications of the 3GPP (Third Generation Partnership Project). As regards the 3G-324M specifications, reference may be made to 3GPP standards TS26.111, TS26.112 and TR26.911.
On the other hand, there is a move to implement video phone services or multimedia services using a mobile IMS (IP Multimedia Subsystem). A future trend may be towards integrating services on a mobile IMS network. As regards the mobile IMS, reference may be made to the 3GPP standard TS23.248.
Patent Document 1 discloses a gateway at a point of connection of a mobile terminal network for multimedia communication under 3GPP and the IP network. In multiplexing a speech and a moving picture from the IP network and transmitting the multiplexed data at a constant period of 64 kbps, the speech as well as the movement is adjusted to an optimum, rate to generate multiplexed data.
Patent Document 2 discloses a conversion apparatus in which, for implementing communication of speech and video between terminals connected to different networks, such as a circuit switched network and an IP network, control information is converted to enable the communication to be established even in case a codec of a terminal differs from that of the other terminal.
Patent Document 3 discloses a configuration including a video phone system which includes a gateway, an IP video phone terminal, connected to the gateway via an IP network, and an IP video phone terminal for a switched network, connected to the gateway over a switched network.
Patent Document 4 discloses a communication system in which an agent that exercises data communication control is provided in each of a server and a client, and in which another agent for controlling the data communication is provided in a gateway which is arranged on a network and to which are connected the server and the client. The information on the processing capability of the client terminal is acquired and data to be transmitted from the server terminal to the client is converted for transmission/reception.
[Patent Document 1] JP Patent Kokai Publication No. JP-P2006-74555A
[Patent Document 2] JP Patent Kokai Publication No. JP-P2006-165935A
[Patent Document 3] JP Patent Kokai Publication No. JP-P2008-42767A
[Patent Document 4] JP Patent Kokai Publication No. JP-A-11-55324